AGES OF GLOBULAR-CLUSTERS - A NEW APPROACH

We have used a new method to analyse the horizontal branch (HE) morpho logy in relation to the distribution of stars near the red giant branc h (RGB) tip for the globular clusters M22, M5, M68, M107, M72, M92, M3 and 47 Tuc, This new method permits the determination of the cluster ages to greater accuracy than does conventional isochrone fitting, Usi ng the method in conjunction with our new high-quality photometric dat a for RGB and HE stars in the first five of these clusters, we discuss the origins of the spread in colour on the HB and its relation to the 'second parameter' problem. The oldest clusters in our sample are fou nd to have relatively low ages (13.5 +/- 2 Gyr). A 1 sigma uncertainty in each of the parameters of mass and helium content, combined with t he effects of helium diffusion, gives a lower limit for the age of the oldest clusters of 9.7 Gyr.